This invention relates to antennas.
There is considerable advantage in being able to use the aperture of an antenna at several different frequency bands simultaneously. In reflector antennas this is often achieved by mounting several feed horns about the focus, albeit with some degradation of pattern characteristics.
In array antennas which are required to operate at several frequencies there are two methods which are applicable, one is to use an interleaved thinned matrix of radiators which has the disadvantage that at neither frequency is the full array gain realisable and the excitation functions are restricted in form; the other method is to arrange for the elements to radiate simultaneously all the frequencies concerned. This has the advantage that the full gain of the aperture is available at both frequencies and also that there is no restriction on the excitation functions usable (within the constraints of the aperture).